1. Field of the Invention
The present invention relates to a color image processing apparatus for processing a color image signal representing a color image.
2. Related Background Art
In order to process a color image electrically, it is well known that a color image signal is formed by reading the color image with a plurality of sensors having different spectral-response characteristics. The assignee of the present invention has proposed a constitution of reading a color image with a plurality of sensors having different spectral-response characteristics, in U.S. Pat. Nos. 4,974,072, 4,953,014 and 4,985,760.
In these documents, a CCD having line filters of athree-line pattern B (blue), G (green) and R (red) is used, as shown in FIG. 6. Accordingly, a portion at a black edge is colored due to the difference in MTF (Modulation Transfer Function) between sensors having different spectral-response characteristics, so that there is an adverse effect on the decision of saturation. That is, as shown in FIG. 16A, a G (green) signal rises up sharply, while a B (blue) signal rises up gradually. As a result, while the points A and B should gray, whereas actually, the peripheral region may become greenish, and the internal region bluish.
In addition to the above color aberration due to difference of MTF, there is a color aberration caused by physical misregistrations of sensors. That is, the CCD of three lines is used as shown in FIG. 6, temporal correction (insertion of a delay circuit) is necessary because the focusing position of each sensor is different. However, as mechanical vibration cannot be suppressed, the phase of each signal becomes slightly displaced, as shown in FIG. 15A. Specifically, considering R (red) and G (green) as shown in FIG. 15, even with the same shape of sensor, the line becomes reddish at point A and bluish at point B, so that a portion of black edge yields some color aberration.
As above described, the color aberration caused by differences in MTF for a three-line sensor or mechanical vibration has a disadvantage of bringing about many inconveniences in various image processings performed at later stages.